Pneumocystis carinii is an important cause of morbidity and mortality in immunocompromised patients, with the highest attack rate occurring in patients with the acquired immunodeficiency syndrome (AIDS). Recent publications suggest that P. carinii may also be a prominent pathogen in pneumonias occurring in normal infants and children as well. Currently, little is known about the immunopathogenesis of P. carinii (PCP) in caring for immunocompromised patients, such an assay would allow for the generation of reliable epidemiologic data dealing with the possible transmission of this infection and the incidence of PCP in non- immunocompromised individuals. Elucidation of the immunopathogenesis of PCP may allow for the development of alternate strategies to interrupt or treat this infection. The long-term objective of this proposal is (1) the development of a reliable non-invasive assay for PCP, and (2) the delineation of the antigenic composition of P. carinii and immunopathogenesis of PCP. This will be accomplished through the production of specific monoclonal antibodies (MAB), especially MAB directed to P. carinii of human origin. These MAB will be used to develop immunoassays for P. carinii antigens and in the analysis of P. carinii surface antigens. Animal models of PCP will be employed to further define the role of both cellular and humoral immunity to these surface antigens in protection or recovery from PCP. Successful completion of this project will aid in the presentation, diagnosis and treatment of PCP.